[2] State Highway 168 was designated in 1932-1934 along a route similar to the present SH 42, but using a number of different roadways.

SH 168 then jogged west on South Boulder Road across the railroad to Louisville's Main Street, and turned east on Pine Street, crossing SH 42 onto Empire Road.

[3] In 1953 the state highway system was greatly reduced[4] and SH 168 disappeared.

The loop through Louisville returned to the system in 1960-1961 with a new number: State Highway 42.

Two new segments of road were built in about 1970, giving SH 42 its current shape (but initially a sweeping curve carried traffic around the corner east of downtown Louisville).